1. Field of the Invention
This invention relates to improvements in an internal combustion engine of the split type operable on less than all of its cylinders when the engine load is below a given value.
2. Description of the Prior Art
In general, internal combustion engines demonstrate higher efficiency and thus higher fuel economy when running under higher load conditions. In view of this fact, split type internal combustion engines have already been proposed which have active cylinders which are always active and inactive cylinders which are inactive when the engine load is below a given value. Such split engines have an intake passage divided into first and second branches, the first branch being associated with the active cylinders and the second branch being associated with the inactive cylinders and in which there is provided a stop valve. In the present invention, a split engine operating system is provided which is responsive to a drop in the engine load below a given value to close the stop valve in the second branch of the intake passage so as to cut off the flow of air to the inactive cylinders and also to cut off the flow of fuel to the inactive cylinders while doubling the amount of fuel supplied to the active cylinders so as to shift the engine into a split engine mode of operation where the engine operates only on the active cylinders. This increases active cylinder loads, resulting in higher fuel economy.
One difficulty with such split type internal combustion engines is that a sudden torque change occurs which imparts a jolt to the passenger when the engine operation is shifted between the split and full engine modes. It is conventional practice to change the air/fuel ratio when the engine operation is shifted between the split and full engine modes so as to suppress such a torque change. However, this requires a special circuit for controlling the air/fuel ratio when the engine mode is changed.